Synergistic effects in the co-pyrolysis of thermoset epoxy resin and biomass on kinetics and product distribution

With the rapid growth of wind power, batteries, and aerospace industries, sustainable disposal of thermoset plastics has become a long-term concern. However, pyrolysis, a highly promising solution for this issue, has seen limited studied on thermoset plastics. Drawing inspiration from the synergistic interactions observed between thermoplastics and biomass, this study explored the co-pyrolysis of a thermoset epoxy resin, diglycidyl ether of bisphenol A, cured with 4,4 '-Diaminodiphenylmethane, with ash-free biomass pseudo-components (cellulose, lignin, and xylan) using thermogravimetry and Py-GC/MS. The results revealed distinctive synergistic effects in Epoxy-Cellulose and Epoxy-Lignin mixtures, delaying the onset and hastening the conclusion of weight loss. This was accompanied by increased activation energies, assessed through the Friedman and Kissinger-Akahira-Sunose methods, as well as higher char yields. Conversely, in Epoxy-Xylan, synergistic effects led to reduced activation energy across most alpha values, resulting in a lower onset temperature and a heightened maximum rate of mixture degradation. Regarding product distribution, all three pseudo-components, particularly lignin, enhanced the selectivity of bisphenol A. Additionally, cellulose and xylan altered the kinetics of N-C and C(N)-C(OH) bond cleavage, reducing the amount and altering the distribution of 2-B-N compounds (compounds featuring two benzene rings and nitrogen). Conversely, the presence of resin reduced the volatiles from cellulose and xylan, promoting phenol-type products and -H and alkylene side chains while diminishing guaiacol-type products and alkyl side chains. Three mechanisms were proposed to elucidate these observed synergistic effects: catalytic effects of -OH groups from biomass pseudo-components, hydrogen exchange or hydrogen bonding between resin-derived nitrogen and biomass-derived oxygen-containing functional groups, and radical reactions. These insights into the co-pyrolysis of biomass and cured epoxy resin can inform the selection of suitable feedstocks for various applications.